In conventional xerography, a xerographic surface comprising a layer of photoconductive insulating material affixed to a conductive backing is used to support latent electrostatic images. In the process, the xerographic surface is electrostatically charged and the charged surface is then exposed to a light pattern of the image being reproduced to thereby discharge the surface in the areas where light strikes the surface. The undischarged areas of the surface thus form an electrostatic charge pattern conforming to the original pattern.
The latent electrostatic image is then developed by contacting it with a finely divided electrostatically attractable powder referred to hereinafter as "toner". The toner is held on the image areas by the electrostatic charge on the layer. Where the charge is greater, the greater amount of toner is deposited. Thus, a toner image is produced in conformity with a light image of the copy being reproduced. The developed image is then generally transferred to a suitable transfer member and the image affixed thereto to form a permanent record of the original document.
In the practice of xerography, the transfer member, ordinarily copy paper, is caused to move in synchronized contact with the photoconductive surface. During this time, an electrical potential opposite from the polarity on the toner is applied to the side of the paper remote from the photoconductive surface to electrostatically attract the toner image from the xerographic surface to the copy paper.
The copy paper, which is an insulator, retains the charge, while inducing a reverse charge in the nondischarged areas of the xerographic surface. This charge orientation creates an electrostatic bond between the paper and xerographic surface. Removal of the copy sheet and the toner image loosely adhering thereto has long been a problem in the xerographic art.
Numerous devices have been employed with varying degrees of success to remove copy sheets from the photoconductive surface in automatic xerographic reproduction apparatus. Probably one of the best known and most widely used devices is an air puffer. The copy sheet is stripped from the surface by introducing a relatively high pressure stream of air between the copy sheet and the surface to overcome the attraction between the paper and the surface.
However, when high air pressures are employed, the air tends to agitate the unfused toner image on the paper and disrupt the image configuration of the toner on the copy sheet. This exhibits itself as smears on the final copy. This blowing of toner powder may also result in toner dust problems in that the air stream broadcasts loose toner particles throughout the reproduction apparatus. Further, because of the volume and velocity of the air stream required to perform the stripping operation, puffer devices are inherently noisy and therefore undesirable.
Another technique for separating copy sheets from a xerographic surface is to mechanically wedge the copy sheet from the xerographic surface by means of mechanical picker fingers. However, since the fingers must of necessity be wedged between the photoconductive surface and the paper adhering thereto, the fingers have a tendency to scratch and abrade the xerographic surface.
Another method for removing copy sheets from the xerographic surface is to provide a vacuum stripping device for pulling the leading edge of the copy sheet from the xerographic surface for subsequent movement of the copy sheet away from the xerographic surface by a suitable paper transport. Problems may be encountered with this type of device in that the amount of vacuum required to strip the paper may be extremely high and the noise created by the air flow may be excessive. Further, the required spacing between the xerographic surface, the vacuum pickoff device, and the subsequent transport all give rise to areas wherein the paper may be jammed or deflected out of the desired paper path.
To minimize the air pressure or vacuum required for stripping the paper by "puffing" or vacuum, a corona discharge device may be utilized to reduce the electrostatic charge on the paper after transfer. In reducing the electrostatic attraction between the paper and the xerographic surface, the attraction between the paper and the toner is also reduced which may result in incomplete transfer of toner from the xerographic surface to the copy paper.